• Measures evaporation rate from a free water surface.
• Used by meteorologists and water engineers throughout the world.
• Manufactured to the American Weather Bureau pattern.
Because of the recognition of the accuracy of this instrument, reliable equations have been devised, by which the readings obtained may be converted into useful figures for evaporation from lakes and reservoirs.
The water level in a standard cylindrical tank (1220 mm diameter) is measured, usually every 24 hours, by adjusting the height of a hook until its point just breaks the surface.
The measurement is taken inside a still-well which provides a small area of warer surface free from ripples. The still0well, made of brass, stands on three levelling screws and has an opening in the base to equalise the water levels inside and out. The hook gauge, also brass, rests on top of the well supported by three horizontal arms, and has a micrometer head to provide very fine adjustment.
A useful accessory is a maximum/minimum thermometer which floats just under the water surface in the main tank. A magnet is supplied for resetting the indices